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Iraq's largest Christian town has been overrun by the same militant Islamists who have gained a foothold in parts of eastern Syria and western and northern Iraq.

The latest advance by ISIS (or the Islamic State, formerly known as the Islamic State in Iraq and Syria) has caused thousands of Christians in the city to flee, just as other minority groups targeted by ISIS have done, as well as Shiite Muslims.

The French government confirmed that the Iraqi city of Qaraqosh has fallen into the hands of the militant al Qaeda offshoot.

"France is highly concerned about the latest progress of ISIS in the North of Iraq and by the taking of Qaraqosh, the largest Christian city of Iraq, and the horrible acts of violence that are committed," French Foreign Minister Laurent Fabius said in a statement.

France called for an emergency meeting of the U.N. Security Council to discuss the threat in Iraq.

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When ISIS took over Mosul, many residents from there had fled to Qaraqosh. In Mosul, ISIS issued an ultimatum to Christians living there: Convert to Islam, pay a fine or face "death by the sword."

Three other nearby villages were also attacked overnight and Thursday, local police officials told CNN. Two of the villages -- Bartella and Tall Kayf -- are predominately Christian. Hundreds of Christian families fled to the north, police said.

The third village is Hamadaniya.

Kurdish forces were involved in heavy clashes protecting the area from ISIS.

ISIS seeks to create an Islamic caliphate that stretches from Syria to Iraq. The group has aggressively targeted Iraqi minority religious groups.

Nickolay Mladenov, the special representative of the U.N. secretary-general for Iraq, last month condemned the persecution of Christians, Shia Muslims and Yazidis, as well as the Shabak and Turkmen ethnic minorities.

The Pentagon is considering conducting emergency air drops to the thousands of stranded Yazidis in northern Iraq, a U.S. Defense official told CNN Thursday.

A spokesman for Pope Francis, the Rev. Federico Lombardi, said on Thursday that the pontiff is deeply concerned about the reports coming from northern Iraq.

"Christian communities are particularly affected: a people fleeing from their villages because of the violence that rages in these days, wreaking havoc on the entire region," Lombardi said in a statement.

Lombardi quoted a prayer the Pope offered last month, expressing to the persecuted that "I know how much you suffer, I know that you are deprived of everything."

Most Iraqi Christians are Chaldeans, who are Roman Catholic communicants.